Hydraulic fracturing is a technique commonly used to stimulate the production of oil and gas from subterranean geologic formations of low permeability. The process is carried out by drilling a wellbore that penetrates the formation and provides a sufficiently unimpeded flowpath for the hydrocarbons to reach the surface. In such treatments, aqueous treatment fluids (also known as fracturing fluids) are introduced into the subterranean formation under sufficient pressure and having sufficient viscosity to create fractures in the formation and to propagate these fractures out into the formation. The aqueous treatment fluids may contain entrained proppants, such as sand or sintered bauxite, so that as the aqueous treatment fluid seeps into the formation, the fractures close upon the proppants to maintain the fractures in an open state for increased permeability.
In using certain aqueous treatment fluids, the high viscosity of the fluids should be maintained while the fractures are being created and propagated, in order to aid in transporting the proppants to the farthest reaches of the fractures. After the proppants have been trapped in the fractures, however, it is desirable that the viscosity of the aqueous treatment fluid is quickly reduced to allow the fluid to flow back through the fractures, around the proppants, and back into the wellbore. Compositions utilized to reduce the viscosity of fracturing fluids are commonly called “breakers” or “breaker fluids.”
A breaker may be added to the fractures externally, i.e., separately from the fracturing fluid. Alternatively, an internal breaker may be incorporated into the initial fracturing fluid. Such breakers preferably have a delayed break profile, so that the fracturing fluid does not break prematurely (before the fracturing fluid has been introduced a sufficient distance into the fracture) or too late (causing slow recovery of the fracturing fluid and/or dislodging of proppant).
Breakers have previously included oxidizers, acids, and enzymes that degrade the polymeric gel structure of fracturing fluids.
U.S. Pat. No. 3,922,173 is directed to processes for producing a controlled reduction in viscosity of aqueous gels when t-butyl hydroperoxide is used as a breaker.
U.S. Pat. No. 5,447,199 is directed to breakers comprising organic peroxides that have a water solubility of about 1 g/100 g or less.
U.S. Pat. No. 8,383,557 is directed to breaker compositions in the form of oil-water emulsions.
U.S. Publication No. 2008/0202758 is directed to breaker compositions that include an organic peroxide and a diluent comprising an organic solvent.
U.S. Publication No. 2011/0247821 is directed to breaker compositions comprising oxidative components and ester components.
U.S. Publication No. 2013/0324445 is directed to breaker compositions that are microemulsions or nanoemulsions.
A common problem with breakers is the eventual “rehealing” of the fracturing fluid. Even though the fracturing fluid has a decreased viscosity at bottom hole temperatures after being broken, the fluid “reheals” or gains viscosity when cooled. This causes great difficulty in drawing fluids back through the fractures to the surface. There remains a need for breaker compositions and methods that inhibit, retard, and/or substantially prevent rehealing of fracturing fluids in subterranean treatment operations when the temperature is reduced.